Bluetooth: Fix locking in bt_accept_enqueue() for BH context

This change “Bluetooth: Fix locking in bt_accept_enqueue() for BH context” in Linux kernel is authored by Matthias Kaehlcke <mka [at]> on Wed Jan 2 16:11:20 2019 -0800.

Bluetooth: Fix locking in bt_accept_enqueue() for BH context

With commit e16337622016 ("Bluetooth: Handle bt_accept_enqueue() socket
atomically") lock_sock[_nested]() is used to acquire the socket lock
before manipulating the socket. lock_sock[_nested]() may block, which
is problematic since bt_accept_enqueue() can be called in bottom half
context (e.g. from rfcomm_connect_ind()):

[<ffffff80080d81ec>] __might_sleep+0x4c/0x80
[<ffffff800876c7b0>] lock_sock_nested+0x24/0x58
[<ffffff8000d7c27c>] bt_accept_enqueue+0x48/0xd4 [bluetooth]
[<ffffff8000e67d8c>] rfcomm_connect_ind+0x190/0x218 [rfcomm]

Add a parameter to bt_accept_enqueue() to indicate whether the
function is called from BH context, and acquire the socket lock
with bh_lock_sock_nested() if that's the case.

Also adapt all callers of bt_accept_enqueue() to pass the new

- l2cap_sock_new_connection_cb()
  - uses lock_sock() to lock the parent socket => process context

- rfcomm_connect_ind()
  - acquires the parent socket lock with bh_lock_sock() => BH

- __sco_chan_add()
  - called from sco_chan_add(), which is called from sco_connect().
    parent is NULL, hence bt_accept_enqueue() isn't called in this
    code path and we can ignore it
  - also called from sco_conn_ready(). uses bh_lock_sock() to acquire
    the parent lock => BH context

Fixes: e16337622016 ("Bluetooth: Handle bt_accept_enqueue() socket atomically")
Signed-off-by: Matthias Kaehlcke <>
Reviewed-by: Douglas Anderson <>
Signed-off-by: Marcel Holtmann <>

This Linux change may have been applied to various maintained Linux releases and you can find Linux releases including commit c4f5627.

There are 24 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 include/net/bluetooth/bluetooth.h |  2 +-
 net/bluetooth/af_bluetooth.c      | 16 +++++++++++++---
 net/bluetooth/l2cap_sock.c        |  2 +-
 net/bluetooth/rfcomm/sock.c       |  2 +-
 net/bluetooth/sco.c               |  2 +-
 5 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/include/net/bluetooth/bluetooth.h b/include/net/bluetooth/bluetooth.h
index ec9d6bc..fabee6d 100644
--- a/include/net/bluetooth/bluetooth.h
+++ b/include/net/bluetooth/bluetooth.h
@@ -276,7 +276,7 @@ int  bt_sock_stream_recvmsg(struct socket *sock, struct msghdr *msg,
 int  bt_sock_wait_state(struct sock *sk, int state, unsigned long timeo);
 int  bt_sock_wait_ready(struct sock *sk, unsigned long flags);
-void bt_accept_enqueue(struct sock *parent, struct sock *sk);
+void bt_accept_enqueue(struct sock *parent, struct sock *sk, bool bh);
 void bt_accept_unlink(struct sock *sk);
 struct sock *bt_accept_dequeue(struct sock *parent, struct socket *newsock);
diff --git a/net/bluetooth/af_bluetooth.c b/net/bluetooth/af_bluetooth.c
index deacc52..8d12198 100644
--- a/net/bluetooth/af_bluetooth.c
+++ b/net/bluetooth/af_bluetooth.c
@@ -154,15 +154,25 @@ void bt_sock_unlink(struct bt_sock_list *l, struct sock *sk)
-void bt_accept_enqueue(struct sock *parent, struct sock *sk)
+void bt_accept_enqueue(struct sock *parent, struct sock *sk, bool bh)
 	BT_DBG("parent %p, sk %p", parent, sk);
-	lock_sock_nested(sk, SINGLE_DEPTH_NESTING);
+	if (bh)
+		bh_lock_sock_nested(sk);
+	else
+		lock_sock_nested(sk, SINGLE_DEPTH_NESTING);
 	list_add_tail(&bt_sk(sk)->accept_q, &bt_sk(parent)->accept_q);
 	bt_sk(sk)->parent = parent;
-	release_sock(sk);
+	if (bh)
+		bh_unlock_sock(sk);
+	else
+		release_sock(sk);
diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index 686bdc6..a3a2cd5 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -1252,7 +1252,7 @@ static struct l2cap_chan *l2cap_sock_new_connection_cb(struct l2cap_chan *chan)
 	l2cap_sock_init(sk, parent);
-	bt_accept_enqueue(parent, sk);
+	bt_accept_enqueue(parent, sk, false);
diff --git a/net/bluetooth/rfcomm/sock.c b/net/bluetooth/rfcomm/sock.c
index aa0db1d..b1f49fc 100644
--- a/net/bluetooth/rfcomm/sock.c
+++ b/net/bluetooth/rfcomm/sock.c
@@ -988,7 +988,7 @@ int rfcomm_connect_ind(struct rfcomm_session *s, u8 channel, struct rfcomm_dlc *
 	rfcomm_pi(sk)->channel = channel;
 	sk->sk_state = BT_CONFIG;
-	bt_accept_enqueue(parent, sk);
+	bt_accept_enqueue(parent, sk, true);
 	/* Accept connection and return socket DLC */
 	*d = rfcomm_pi(sk)->dlc;
diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c
index 529b389..9a58099 100644
--- a/net/bluetooth/sco.c
+++ b/net/bluetooth/sco.c
@@ -193,7 +193,7 @@ static void __sco_chan_add(struct sco_conn *conn, struct sock *sk,
 	conn->sk = sk;
 	if (parent)
-		bt_accept_enqueue(parent, sk);
+		bt_accept_enqueue(parent, sk, true);
 static int sco_chan_add(struct sco_conn *conn, struct sock *sk,

The commit for this change in Linux stable tree is c4f5627 (patch).

Leave a Reply

Your email address will not be published. Required fields are marked *